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Date:	Tue, 20 Mar 2007 12:17:02 +0100
From:	Jarek Poplawski <jarkao2@...pl>
To:	Folkert van Heusden <folkert@...heusden.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>,
	Neil Brown <neilb@...e.de>, Christoph Hellwig <hch@....de>,
	Jan Kara <jack@...e.cz>
Subject: dquot.c: possible circular locking Re: [2.6.20] BUG: workqueue leaked lock

On 15-03-2007 20:17, Folkert van Heusden wrote:
>>> On Tue, 13 Mar 2007 17:50:14 +0100 Folkert van Heusden <folkert@...heusden.com> wrote:
...
> Haha ok :-)
> 
> Good, since I run 2.6.20 with these debugging switches switched on, I
> get occasionally errors like these. I get ALWAYS the following error
> when the system first boots when the TOR executable is started:
> 
> [  137.324255] =======================================================
> [  137.324359] [ INFO: possible circular locking dependency detected ]
> [  137.324412] 2.6.20 #2
> [  137.324457] -------------------------------------------------------
> [  137.324510] tor/4857 is trying to acquire lock:
> [  137.324559]  (tty_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa
> [  137.324765]
> [  137.324766] but task is already holding lock:
> [  137.324859]  (&s->s_dquot.dqptr_sem){----}, at: [<c1099403>] dquot_alloc_space+0x50/0x189
> [  137.325067]
> [  137.325069] which lock already depends on the new lock.

IMHO lockdep found that two locks are taken in different order:

-> #1: 1) tty_mutex in con_console() 2) dqptr_sem (somewhere later)
-> #0: 1) dqptr_sem 2) tty_console in dquot_alloc_space() with print_warning()

Probably print_warning() and flush_warnings() should be reworked
to do printing without dqptr_sem or locking order should be changed.
I hope somebody from this CC can work it out better.

Regards,
Jarek P.


> [  137.325071]
> [  137.325206]
> [  137.325208] the existing dependency chain (in reverse order) is:
> [  137.325300]
> [  137.325301] -> #4 (&s->s_dquot.dqptr_sem){----}:
> [  137.325501]        [<c10354b8>] check_prev_add+0x154/0x206
> [  137.325852]        [<c10355d4>] check_prevs_add+0x6a/0xd5
> [  137.326197]        [<c1036dd2>] __lock_acquire+0x61c/0xa05
> [  137.326538]        [<c1037624>] lock_acquire+0x62/0x81
> [  137.326887]        [<c1032b5f>] down_read+0x2b/0x3d
> [  137.327241]        [<c1099403>] dquot_alloc_space+0x50/0x189
> [  137.327588]        [<c10a98e6>] ext3_new_blocks+0x44b/0x5a2
> [  137.327935]        [<c10abe78>] ext3_alloc_blocks+0x40/0xdf
> [  137.328280]        [<c10abf67>] ext3_alloc_branch+0x50/0x21b
> [  137.328622]        [<c10ac445>] ext3_get_blocks_handle+0x1b8/0x367
> [  137.328980]        [<c10ac76e>] ext3_getblk+0x97/0x228
> [  137.329330]        [<c10ac919>] ext3_bread+0x1a/0x78
> [  137.329672]        [<c10b1bc2>] ext3_mkdir+0xf4/0x270
> [  137.330022]        [<c1072a6a>] vfs_mkdir+0xb3/0x161
> [  137.330368]        [<c1072ba4>] sys_mkdirat+0x8c/0xc4
> [  137.330714]        [<c1072bfc>] sys_mkdir+0x20/0x22
> [  137.331063]        [<c1002f78>] syscall_call+0x7/0xb
> [  137.331406]        [<ffffffff>] 0xffffffff
> [  137.331771]
> [  137.331772] -> #3 (&ei->truncate_mutex){--..}:
> [  137.331979]        [<c10354b8>] check_prev_add+0x154/0x206
> [  137.332332]        [<c10355d4>] check_prevs_add+0x6a/0xd5
> [  137.332676]        [<c1036dd2>] __lock_acquire+0x61c/0xa05
> [  137.333025]        [<c1037624>] lock_acquire+0x62/0x81
> [  137.333370]        [<c1205c09>] __mutex_lock_slowpath+0x75/0x28c
> [  137.333930]        [<c1205b88>] mutex_lock+0x8/0xa
> [  137.334271]        [<c10ae14f>] ext3_truncate+0x170/0x468
> [  137.334613]        [<c1058e72>] vmtruncate+0xa6/0x116
> [  137.334949]        [<c107d587>] inode_setattr+0x145/0x16c
> [  137.335286]        [<c10af071>] ext3_setattr+0x150/0x22f
> [  137.335627]        [<c107d909>] notify_change+0x35b/0x392
> [  137.335968]        [<c10679d2>] do_truncate+0x52/0x75
> [  137.336305]        [<c1071f5e>] may_open+0x1ec/0x231
> [  137.336642]        [<c107211c>] open_namei+0xda/0x59b
> [  137.336975]        [<c106863a>] do_filp_open+0x2c/0x53
> [  137.337310]        [<c106896f>] do_sys_open+0x52/0xd8
> [  137.337645]        [<c1068a11>] sys_open+0x1c/0x1e
> [  137.337980]        [<c1002f78>] syscall_call+0x7/0xb
> [  137.338315]        [<ffffffff>] 0xffffffff
> [  137.338665]
> [  137.338666] -> #2 (&inode->i_alloc_sem){--..}:
> [  137.338864]        [<c10354b8>] check_prev_add+0x154/0x206
> [  137.339200]        [<c10355d4>] check_prevs_add+0x6a/0xd5
> [  137.339535]        [<c1036dd2>] __lock_acquire+0x61c/0xa05
> [  137.339200]        [<c10355d4>] check_prevs_add+0x6a/0xd5
> [  137.339535]        [<c1036dd2>] __lock_acquire+0x61c/0xa05
> [  137.339874]        [<c1037624>] lock_acquire+0x62/0x81
> [  137.340207]        [<c1032bf5>] down_write+0x2b/0x45
> [  137.340545]        [<c107d890>] notify_change+0x2e2/0x392
> [  137.340886]        [<c10679d2>] do_truncate+0x52/0x75
> [  137.341222]        [<c1071f5e>] may_open+0x1ec/0x231
> [  137.341557]        [<c107211c>] open_namei+0xda/0x59b
> [  137.341898]          [<c1068a11>] sys_open+0x1c/0x1e
> [  137.343109]        [<c1002f78>] syscall_call+0x7/0xb
> [  137.343444]        [<ffffffff>] 0xffffffff
> [  137.343792]
> [  137.343793] -> #1 (&sysfs_inode_imutex_key){--..}:
> [  137.343988]        [<c10354b8>] check_prev_add+0x154/0x206
> [  137.344320]        [<c10355d4>] check_prevs_add+0x6a/0xd5
> [  137.344655]        [<c1036dd2>] __lock_acquire+0x61c/0xa05
> [  137.344986]        [<c1037624>] lock_acquire+0x62/0x81
> [  137.345321]        [<c1205c09>] __mutex_lock_slowpath+0x75/0x28c
> [  137.345658]        [<c1205b88>] mutex_lock+0x8/0xa
> [  137.345991]        [<c10a5447>] sysfs_hash_and_remove+0x43/0x11c
> [  137.346328]        [<c10a5ef7>] sysfs_remove_file+0xd/0x12
> [  137.346660]        [<c114b00c>] device_remove_file+0x32/0x44
> [  137.346992]        [<c114b6d9>] device_del+0x174/0x1d2
> [  137.347325]        [<c114b742>] device_unregister+0xb/0x15
> [  137.347661]        [<c114b93d>] device_destroy+0x8d/0x9a
> [  137.347994]        [<c1137a38>] vcs_remove_sysfs+0x1c/0x38
> [  137.348328]        [<c113e0d8>] con_close+0x5e/0x6b
> [  137.348661]        [<c1130103>] release_dev+0x4c4/0x6ce
> [  137.348999]        [<c113077b>] tty_release+0x12/0x1c
> [  137.349332]         [<c10aa723>] ext3_file_write+0x2d/0xba
> [  137.358495]        [<c1069441>] do_sync_write+0xc7/0x116
> [  137.358838]        [<c1069612>] vfs_write+0x182/0x187
> [  137.359176]        [<c10696b8>] sys_write+0x3d/0x64
> [  137.359513]        [<c1002f78>] syscall_call+0x7/0xb
> [  137.359848]        [<ffffffff>] 0xffffffff
> [  137.360200]
> [  137.360202] other info that might help us debug this:
> [  137.360204]
> [  137.360335] 3 locks held by tor/4857:
> [  137.360382]  #0:  (&inode->i_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa
> [  137.360625]  #1:  (&ei->truncate_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa
> [  137.361072]  #2:  (&s->s_dquot.dqptr_sem){----}, at: [<c1099403>] dquot_alloc_space+0x50/0x189
> [  137.361313]
> [  137.361314] stack backtrace:
> [  137.361401]  [<c1003d57>] show_trace_log_lvl+0x1a/0x30
> [  137.361488]  [<c1003d7f>] show_trace+0x12/0x14
> [  137.361571]  [<c1003e79>] dump_stack+0x16/0x18
> [  137.361663]  [<c1034d6d>] print_circular_bug_tail+0x6f/0x71
> [  137.361752]  [<c1035398>] check_prev_add+0x34/0x206
> [  137.361838]  [<c10355d4>] check_prevs_add+0x6a/0xd5
> [  137.362786]  [<c1036dd2>] __lock_acquire+0x61c/0xa05
> [  137.362877]  [<c1037624>] lock_acquire+0x62/0x81
> [  137.362960]  [<c1205c09>] __mutex_lock_slowpath+0x75/0x28c
> [  137.363047]  [<c1205b88>] mutex_lock+0x8/0xa
> [  137.363132]  [<c1098d79>] print_warning+0x8c/0x15d
> [  137.363217]  [<c1099537>] dquot_alloc_space+0x184/0x189
> [  137.363302]  [<c10a98e6>] ext3_new_blocks+0x44b/0x5a2
> [  137.363391]  [<c10abe78>] ext3_alloc_blocks+0x40/0xdf
> [  137.363476]  [<c10abf67>] ext3_alloc_branch+0x50/0x21b
> [  137.363561]  [<c10ac445>] ext3_get_blocks_handle+0x1b8/0x367
> [  137.363650]  [<c10ac66c>] ext3_get_block+0x78/0xe3
> [  137.363735]  [<c108a239>] __block_prepare_write+0x168/0x3fd
> [  137.363822]  [<c108ad10>] block_prepare_write+0x28/0x3b
> [  137.363908]  [<c10acbcd>] ext3_prepare_write+0x3f/0x18d
> [  137.363996]  [<c104dbe5>] generic_file_buffered_write+0x197/0x5e6
> [  137.364084]  [<c104e2e2>] __generic_file_aio_write_nolock+0x2ae/0x5ad
> [  137.364171]  [<c104e6ea>] generic_file_aio_write+0x58/0xc4
> [  137.364254]  [<c10aa723>] ext3_file_write+0x2d/0xba
> [  137.364340]  [<c1069441>] do_sync_write+0xc7/0x116
> [  137.364425]  [<c1069612>] vfs_write+0x182/0x187
> [  137.364511]  [<c10696b8>] sys_write+0x3d/0x64
> [  137.364595]  [<c1002f78>] syscall_call+0x7/0xb
> [  137.364682]  =======================
> 
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